physics exam

The forces acting on a child sitting in a seat are described by the free-body diagram shown. What is the net force acting on the child?

0 N

A child on a spinning ride at a playground has a centripetal acceleration of 0.80 m/s2. The child completes a full circle every 4.2 s. How far from the center of the ride is the child?

0.36 m

If 3,600 J of work is done in 3.0 s, what is the power?

1,200 W

An elevator has a weight of 14,700 N and has an acceleration of -0.30 m/s2. The free-body diagram shows the forces acting on the elevator. To the nearest whole number, what is the force of tension, Ft, acting on the elevator?

14,250 N

A spring that has a spring constant of 1400 N/m is stretched to a length of 2.5 m. If the normal length of the spring is 1.0 m, how much elastic potential energy is stored in the spring?

1575 J

Sixty-three joules of heat are added to a closed system. The initial internal energy of the system is 58 J, and the final internal energy is 93 J. How much work is being done by the system?

28 J

A bicycle tire has a radius of 0.23 m. The tire spins at a constant speed with a centripetal acceleration of 42 m/s2. What is the tangential speed of the tire?

3.1 m/s

A heat engine has a temperature of 1800 K. Some of the heat from the engine flows to the surroundings, which are at a temperature of 160 K. What is the approximate efficiency of the engine?

91%

The acceleration due to gravity on Mercury is 3.7 m/s2, which is about six times the acceleration due to gravity on Pluto. Which statement accurately compares the mass and weight of an object on these two planets?

An object weighs about one-sixth as much but has the same mass on Pluto as on Mercury.

Suppose the exhaust system on a heat engine is not functioning properly. Which statement best explains how this will affect the engine?

Burned gases will not be released into the surrounding air.

Earth and all of the air in the atmosphere around it make up an incredibly complex system. Energy is constantly changing forms in many different ways. How would scientists most likely describe the system of the Earth in regard to energy?

Earth is an open system because heat energy from the Sun enters through the atmosphere.

Jin knows that the initial internal energy of a closed system is 78 J and the final internal energy is 180 J. He also knows that 64 J of energy are used to do work. To find the heat added to the system, Jin completes the steps below. 1. Add the initial internal energy plus the final internal energy to find the change in internal energy. 2. Add the change in internal energy to the energy used to do work. 3. Write the answer in joules. Which best describes Jin's error?

For step 1, he should have subtracted 78 J from 180 J to find the change in internal energy.

What did Johannes Kepler contribute to the study of planets?

He provided mathematical support for the heliocentric model.

Substance X transfers thermal energy to substance Y through conduction. What is an accurate conclusion about the condition of both substances before conduction occurred?

Substance X's molecules were faster than substance Y's.

Suchita is going to make an energy transfer diagram to represent the energy transformations associated with the flame of a gas stove. The diagram will show that the chemical energy of the fuel transforms into 50 J of chemical energy, 400 J of heat, and 200 J of light. Which statement describes Suchita's final diagram?

The arrow for heat is the widest output arrow.

According to the first law of thermodynamics, what could happen when heat is added to a system?

The heat is turned into work done by the system.

A boy is running to the east and jumps into a stationary boat in a lake. Once the boy lands in the boat, the boat moves to the east. Which best compares the initial momentum of the boy with the final momentum of the boy/boat system?

The initial momentum of the boy is equal to the boy/boat because the final velocity of the boat is less than the initial velocity of the boy.

In an aerosol can used for spray paint, a highly compressed "propellant" helps move the liquid into a "dip tube" so that it can be sprayed out. The valve through which the liquid sprays is usually closed, but when it is pressed down, it opens and allows material to pass through. Why does the liquid rise up through the dip tube when the valve is opened?

The propellant gas wants to expand as much as it can, so if the valve is open, the propellant expands and pushes the spray up out of the can making more room for itself to expand.

The image shown is an illustration of Kepler's second law. Which conclusion is best supported by the image?

The time needed to travel from W to X is the same as the time needed to travel from Y to Z.

Why are the action and reaction forces described by Newton's third law of motion excluded in the free-body diagram of an object?

They act on different objects, so they would not appear together.

According to Newton's second law of motion, the acceleration of an object is inversely proportional to which quantity?

mass

A substance will have a relatively rigid, unchanging shape when it is a

solid.

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?

velocity and displacement

Four landing sites are proposed for a lander. Data about the sites are listed in the table. At which landing site would the lander have the greatest amount of gravitational potential energy?

x

An object moving in a circle is represented by the motion map. Based on the map, at which point is the object accelerating toward the right?

z